1. Field of the Invention
The present invention relates to a method of and apparatus for the repair of turbine blades and is primarily concerned with repair of turbine blades in which the turbine blade assembly has a plurality of blades interconnected by means of connecting members, such connecting members may, for example, comprise lacing wires or cover bands. Such connecting members require a hole or other recess in the turbine blade to connect the connecting members to each blade.
The interconnecting members prevent excessive relative movement between the blades and dampen vibration during operation of the turbine.
The invention is primarily concerned with turbine blades provided with lacing wire holes, the lacing wires may be wires, rods, tubes or other members and will hereinafter be referred to, for the sake of convenience only, as lacing wires.
In use of the turbine the blades are subjected to wear and damage due to the adverse environment in which they have to operate. After a period of use, some repair work or renovation to the blades of the turbine becomes necessary.
It has been proposed by the applicants to carry out work on the turbine blades whilst the blades are still in place on the rotor. Such "in situ" repairs, providing they can be carried out satisfactorily considerably decreases the period in which the rotor has to be out of operation and, since the removal of the blades from the rotor is not only a time consuming and hence expensive operation, but also can lead to further damage being caused to the blades and/or rotor.
It has been found by the applicant, and is described in British patent specification 2091139, that where repair work has to be carried out in the vicinity of lacing wire holes, which repair work involves the input of considerable thermal energy and necessitates heat treatment after repair, an improved repair is provided by filling each lacing wire hole to eliminate the discontinuity in the blade afforded thereby.
Whereas such an operation can be carried out without difficulty when a blade has been removed from the rotor, and indeed in some cases it is not unduly difficult to fill the lacing wire holes even while the blade is on the rotor, the subsequent re-drilling of the lacing wire hole presents enormous problems. The lacing wire hole axis is generally at an angle considerably inclined to the surface of the blade, the blades in some rotors may have a considerable length and tend to move fairly easily when any pressure is applied thereto. It is essential that the lacing wire hole is drilled in the correct position, otherwise this would distort the lacing wires from their intended path which will have the effect in use of the turbine of applying a considerable strain to the blade resulting in an area of highly concentrated stress on that blade due to an out-of-alignment lacing wire hole.